Ecological succession and fine sediment accretion influence local patch dynamics of a pioneer riparian species (Typha minima Hoppe)

Changes in environmental variables induced by ecological succession and hydrogeomorphological processes affects riparian vegetation dynamics along rivers. The biotic and abiotic factors driving local patch dynamics of riparian species is little known for early successional stages. To fill this gap, we examined local patch dynamics and frequency of occurrence of a protected riparian pioneer species (Typha minima Hoppe) and related it to several biotic and abiotic variables along the Isère River (France) from 2016 to 2019. We monitored biotic and abiotic factors related to ecological succession and sediment accretion. We implemented Linear Mixed and Generalized Mixed Models to analyze how environmental factors affected patch boundary dynamics of T. minima. Finally, we built a Structural Equation Model to describe potential relationships between T. minima frequency, height above mean water level, vegetation cover and composition. We found that a thick layer of silt and sand deposits as well as a moderate herbaceous and low shrub cover layer characterized T. minima patch progression close to the mean water level. Typha minima stands did not seem to expand on coarser substrates with lower herbaceous cover. Its maintenance was associated with large silt and sand deposits and high cover of herbaceous plants and shrubs well above the mean water level. The variables characterizing patch regression were not clearly identified. Finally, the interaction between bar height, vegetation cover and succession stage did not explain variations in T. minima frequency. Our results provide knowledge about the environmental variables associated with T. minima patch dynamics, which are useful for future conservation and restoration projects. Habitat rejuvenation through restoration of natural river flow regimes could sustain local T. minima transplantation and large population turnover essential to the conservation of this species.